1. Field of the Invention
This invention relates to liquid filtering and more particularly, to the period washing of the filter cake.
2. Description of the Prior Art
Filtering techniques are well established in the art and for the separation of particulate material from a mother liquor. In some applications a waste product must be removed and disposed of and in others the main product of a process is deposited on the filter. In some instances the mother liquor or soluble particles contained in the filter cake are valuable products which require recovery.
The wash can serve to wash soluble components from the filter cake. The instant invention is not concerned with, or limited to any particular filtering technique or type of filter bed, and has equal applicability to gravity filters, pressure filters or vacuum filters, and equally applies to backwash, throughwash or combination wash techniques. The thrust of the invention is at the maximizing of the efficiency of the wash operation irrespective of the type of filtration operation or filter bed with which the wash is used to remove mother liquor or soluble components sorbed or deposited on the filter or in the filter cake.
Due to the current recognition of the need to prevent polution of our atmosphere and water supplies, rivers and the like, the dumping of waste produce into bodies of water is frequently prohibited or restricted unless the waste product is of such a nature as to not adversely affect the environment. For this reason, in many applications, it is necessary to reduce the quantities of waste being dumped. In other applications, the desire to separate soluble components from the wash liquor is due to the value of the soluble component. High energy and materials costs dictate that the recovery process involve the use of a minimum amount of energy and therefore it is preferable to maximize the ratio of soluble component to wash liquor. The washing techniques typically involve passing as much wash fluid through the filter bed as necessary to separate the soluble constituents from the filter cake. If all of the soluble salt contaminants or products which must be washed from the filter cake were contained in the mother liquor, removal would require one void volume of wash liquor. Heretofore, very little consideration has been paid to the minimizing of the quantity of wash fluid which is used because of the uncertainties of establishing a minimum.